1. Field of the Invention
The present invention relates to a load-cup which receives wafers as they are loaded onto and unloaded from a chemical mechanical polishing apparatus. More particularly, the present invention relates to the pedestal of such a load-cup.
2. Description of the Related Art
Increasing the integration of semiconductor devices has required sequentially depositing multiple layers on a wafer. Accordingly, the semiconductor manufacturing process must include steps for planarizing each layer formed on the semiconductor wafer. Chemical mechanical polishing (CMP) is a typical process used for this purpose. In fact, CMP is well-suited for use in connection with large-diameter wafers because CMP produces excellent uniformity in planarizing wide areas in addition to narrow ones.
The CMP process makes use of mechanical friction and a chemical agent for finely polishing a wafer surface, such as that comprising tungsten or an oxide. In the mechanical aspect of such polishing, a wafer is placed on a rotating polishing pad and is rotated while a predetermined is load applied thereto, whereby the wafer surface is polished by the friction created between the polishing pad and the wafer surface. In the chemical aspect of such polishing, the wafer surface is polished by a chemical polishing agent, referred to as slurry, supplied between the polishing pad and the wafer.
A conventional CMP apparatus will now be described with reference to FIGS. 1-6. As shown best in FIGS. 1 and 2, the conventional CMP apparatus includes a base 100, polishing pads 210a, 210b and 210c installed on the base 100, a load-cup 300 for loading/unloading wafers, and a head rotation unit 400 having a plurality of polishing heads 410a, 410b, 410c and 410d for holding the wafers and fixedly rotating the same on the polishing pads 210a, 210b and 210c. 
In general, the CMP apparatus is provided with three polishing pads 210a, 210b and 210c so that a plurality of wafers can be processed in a short time. Each of the polishing pads 210a, 210b and 210c is closely fixed on a rotatable carousel (not shown). Pad conditioners 211a, 211b and 211c for controlling the surface states of the polishing pads 210a, 210b and 210c and slurry supplying arms 212a, 212b and 212c for supplying slurry to the surfaces of the polishing pads 210a, 210b and 210c are provided in the vicinity of the polishing pads 210a, 210b and 210c. 
The load-cup 300 for wafer loading/unloading has a pedestal 310 having a circular-plate shape, on which the wafers are placed, installed therein. At the load-cup 300, as will be described later, washing of polishing heads 410a, 410b, 410c and 410d for holding wafers and the pedestal 310 is performed.
The head rotation unit 400 includes four polishing heads 410a, 410b, 410c and 410d and four rotation shafts 420a, 420b, 420c and 420d. The polishing heads 410a, 410b, 410c and 410d hold wafers and apply a predetermined pressure to the top faces of the polishing heads 410a, 410b, 410c and 410d for close fixation while polishing is performed. The rotation shafts 420a, 420b, 420c and 420d for rotating the polishing heads 410a, 410b, 410c and 410d, respectively, are mounted on a frame 401 of the head rotation unit 400. Within the frame 401 of the head rotation unit 400 a driving mechanism is provided for rotating the rotation shafts 420a, 420b, 420c and 420d. The head rotation unit 400 is supported by a pivot 402 and is installed to be rotatable around the pivot 402.
Also, the load-cup 300 includes a circular pedestal 310 on which the wafers are placed. The bottom surfaces of the polishing heads 410a, 410b, 410c and 410d and the top surface of the pedestal 310 are washed at the load-cup 300, as will be described later in more detail.
The head rotation unit 400 includes four polishing heads 410a, 410b, 410c and 410d and four rotation shafts 420a, 420b, 420c and 420d. The polishing heads 410a, 410b, 410c and 410d hold wafers and apply a predetermined amount of pressure to the top surfaces of the polishing pads 210a, 210b, 210c and 210d. The rotation shafts 420a, 420b, 420c and 420d for rotating the polishing heads 410a, 410b, 410c and 410d, respectively, are mounted on a frame 401 of the head rotation unit 400. A driving mechanism for rotating the rotation shafts 420a, 420b, 420c and 420d is provided within the frame 401 of the head rotation unit 400. The head rotation unit 400 is supported by a rotary bearing 402 so as to be rotatable about the longitudinal axis of the rotary bearing 402.
The process performed by the CMP apparatus having the above-described configuration will now be described with reference to FIGS. 1 and 2. First, a wafer 10 transferred to the load-cup 300 by a wafer transfer apparatus (not shown) is placed on the surface of the pedestal 310 of the load-cup 300. Here, the wafer 10 is adhered by suction to the surface of the pedestal 310 so as not to move. Then, the wafer 10 is lifted by the pedestal 310 onto a polishing head 410 positioned above the pedestal 310. The wafer 10 is adhered by suction to the polishing head 410. The head rotation unit 400 is rotated to transfer the wafer 10 in such a state above the polishing pad 210a adjacent to the load-cup 300. Then, the polishing head 410 is lowered to tightly press the wafer 10 onto the polishing pad 210a. At this time, the polishing pad 210a and the wafer 10 are rotated in the same direction while slurry is supplied therebetween, whereby the wafer 10 is polished. The wafer 10 is then transferred sequentially to the other polishing pads 210b and 210c and then to the load-cup 300 where it is placed on the pedestal 310. Thereafter, the wafer transfer apparatus transfers the wafer 10 placed on the pedestal 310 to a location outside the CMP apparatus.
Once the wafer 10 has been unloaded, the polishing head 410 descends towards the load-cup 300. In such a state, deionized water is sprayed to wash the bottom surface of the polishing head 410 and the top surface of the pedestal 310. When washing is completed, the polishing head 410 and the pedestal 310 are lifted again and a new wafer is transferred by the wafer transfer apparatus onto the pedestal 310.
FIGS. 3 and 4 are perspective views of the load-cup and pedestal, respectively, of the conventional CMP apparatus. FIG. 5 is a cross-sectional view of the load-cup with its pedestal, and FIG. 6 is an enlarged cross-sectional view of a peripheral portion of the pedestal shown in FIG. 5.
Referring to FIGS. 3 and 5, in order to wash the bottom surface of the polishing head 410 and the top surface of the pedestal 310, the load cup 300 is provided with washing means comprising a first nozzle 331 and a second nozzle 332 for spraying deionized water within a washing basin 320 of the load-cup 300. The first nozzle 331 is oriented so as to spray deionized water toward the top surface of the pedestal 310 and the second nozzle 332 is oriented so as to spray deionized water toward a membrane 411 installed on the bottom surface of the polishing head 410. The membrane 411 allows a vacuum to act on the wafers and secure them to the polishing head 410. Three sets each of the first and second nozzles 135 and 136 are installed at equal angular intervals around the circumference of the pedestal 310. Three wafer aligners 340 for guiding wafers are installed within the washing basin 320 of the load-cup 300 at equal angular intervals around the circumference of the pedestal 310 to guide the wafers placed on the pedestal 310 into position.
The washing basin 320 is supported by a cylindrical support housing 350, and a flexible hose 336 for supplying deionized water to the first and second nozzles 331 and 332 is installed within the support housing 350. A washing fluid channel 337 for connecting the flexible hose 336 to the first and second nozzles 331 and 332 is provided within the washing basin 320.
As best shown in FIG. 4, the pedestal 310 of the load-cup 300 includes a pedestal plate 311, a pedestal support column 312 and a thin pedestal film 313. The pedestal plate 311 serves to support wafers and is in turn supported by the pedestal support column 312. The conventional pedestal plate 311 is circular. The thin pedestal film 313 is adhered to the top surface of the pedestal plate 311 and directly contacts the wafer supported by the pedestal plate 311.
Referring to both FIGS. 4 and 5, a plurality of fluid ports 314 extend through the pedestal plate 311 to allow a wafer to be vacuum-chucked to the plate 311 and to allow deionized water to be sprayed from the plate 311. A vertical passageway 316 extends through the pedestal support column 312, and a lateral passageway 315 defined within the pedestal plate 311 connects the fluid ports 314 to the vertical passageway 316. The vertical passageway 316 and the lateral passageway 315 allow deionized water to be fed to the fluid ports 314 for washing the membrane 411 disposed at the bottom of the polishing head 410.
Therefore, as described above, the load-cup 300 is responsible for washing the bottom surface of the polishing head 410 and the top surface of the pedestal 310 as well as for supporting wafers while they are loaded and unloaded onto and from the CMP apparatus. The washing step is very important in the CMP process. Contaminants such as slurry debris or polished silicon particles are unavoidably produced during the CMP process, and some of the contaminants may remain on the surface of the membrane 411 and/or the pedestal 310. The contaminants remaining on the surface of the membrane 411 and/or the pedestal 310 can generate micro-scratches on the surface of a wafer if the contaminants are transferred thereto when the wafer is loaded in the course of polishing. The micro-scratches may cause defects such as gate oxide leakage or gate line bridging in the semiconductor devices, which lowers the yield and reliability of the semiconductor devices. Thus, any contaminants remaining on the membrane 411 and/or the pedestal 310 must be removed by washing the same using deionized water.
However, such contaminants cannot be completely removed by the washing operation performed by the conventional CMP apparatus.
In an attempt to wash the contaminants off of the membrane 411 disposed at the bottom of the polishing head 410, deionized water is sprayed upwards through the fluid ports 314 of the pedestal plate 311. However, the contaminants washed off of the surface of the membrane drop onto the pedestal film 313 as entrained in the deionized water. Also, some of the contaminants are induced into holes 3131 in the pedestal film 313, which holes 3131 are shown in FIG. 6. These holes 3131 have been punched into the film 313 to lower the rigidity thereof and thus lessen the impact on wafers contacting the film 313. Each of the holes 3131 has a diameter of about 2 mm. The contaminants can therefore enter the holes 3131 and are not readily washed away by deionized water sprayed through the first nozzle 331 of the load-cup 300. Hence, the contaminants may dry up over time in the holes 3131 and thereby form particles each having a diameter of about 20 μm. Both the contaminants entrained in the deionized water remaining on the surface of the pedestal film 313 and the contaminants accumulating in the holes 3131 contact the surface of a wafer loaded onto the CMP apparatus.
In the conventional CMP apparatus, the pedestal film 313 and the wafer contact each other over a wide area because the pedestal film 313 extends over the entire surface of the pedestal plate 311. Accordingly, a comparatively large amount of contaminants are transferred to the wafer surface, i.e., contaminants are transferred to the wafer over practically the entire surface thereof. The contaminants transferred to the wafer surface may produce scratches in the wafer surface during polishing, thereby lowering the yield and reliability of a semiconductor device manufactured from the polished wafer.